Vacuum insulating glazing units (“VIGU”) are known comprising two spaced-apart transparent panes (typically formed of glass) having an evacuated atmosphere therebetween to reduce the thermal conductivity between the panes. Most VIGU assemblies further include a plurality of small objects that are positioned between the panes so as to touch the opposing inside surfaces of the panes. When the enclosed volume between the panes is evacuated of air, these objects maintain the separation between the panes against the forces applied by atmospheric pressure bearing on the external surfaces. These separation-maintaining objects are called a variety of names in the prior art, e.g., pillars and spacers, however, in this application they will be referred to primarily as “stand-off elements” to differentiate them from other items that are in common use in the insulating glass (IG) industry.
In prior art VIGU products, each stand-off element is first individually positioned on one of the two panes and then affixed in place. This positioning of the stand-off elements may be done manually, by robotic “pick and place” machines or other automatic devices, by liquid transport or by screen printing/stenciling. The affixing of the stand-off elements to the pane may be done individually or en masse using, for example, adhesives, tack welding or heating in a furnace. In some cases, the spacers are affixed to both panes of the VIGU. Regardless of the process used, the complexity of individually positioning and affixing stand-off elements is believed to be a significant component in the cost of manufacturing VIGU products. A reduction in manufacturing costs is needed to facilitate the widespread entry of VIGU products into the commercial and residential glazing market.
For a VIGU with a given pane size, vacuum level, pane material and stand-off element material, the total surface area of stand-off elements required to prevent cracking of the panes or crushing of the stand-off elements themselves may be calculated. However, the question of whether to provide this required surface area by using a relatively small number of relatively large (i.e., in projected area) stand-off elements, or alternatively, by using a relatively large number of relatively small stand-off elements, has posed a dilemma for manufacturers. On the one hand, a relatively small number of relatively large stand-off elements is easier (and thus less costly) to manufacture and affix on the pane, however, the larger size makes the stand-off elements more likely to be visible, making the VIGU less desirable from an aesthetic standpoint. On the other hand, a relatively large number of relatively small stand-off elements is more difficult (and thus more costly) to manufacture and affix on the pane, however, the small stand-off elements are less likely to be visible, making the VIGU more aesthetically desirable. A need therefore exists, for VIGU stand-off elements that are easy to manufacture and affix on the pane, even when the stand-off elements are very small in size and very large in number.
It is further known that thermal cycling that is encountered during the life of the VIGU will lead to differential expansion and contraction of the two panes on either side of the stand-offs. In prior art VIGU products having stand-off elements affixed to one pane, the movement of the stand-off elements on the attached pane relative to the unattached pane may result in scratching the inner surface of the unattached pane or wearing of the tips of the stand-offs. In addition, the friction at the tip of the stand-off elements may restrict relative movement between the panes, allowing stresses to build that may crack the panes. A need therefore exists, for VIGU stand-off elements that facilitate differential movement between the panes with reduced wear and friction.